Clinker substitute based on calcined clay

ABSTRACT

A method for producing a clinker substitute for use in cement production includes predrying clay with an iron content &gt;1.5 wt-% in a form of iron oxides and a kaolinite content &lt;40 wt-% to a moisture &lt;10 wt-%. The clay is comminuted to a grain size &lt;2 mm. The clay is calcined by thermal treatment in a furnace at a temperature of 600 to 1000° C. The clay is thermally treated under reducing conditions at a temperature of 600 to 1000° C. so as to form a reduction product. The reduction product is intermediately cooled to a temperature &lt;300° C. and finally cooled.

This invention relates to a clinker substitute, methods for producingthe same, the use thereof, construction materials such as cement, mortarand concrete containing the clinker substitute, and methods forproducing these construction materials.

Cement is a hydraulically hardening construction material which consistsof a mixture of finely ground, non-metallic inorganic constituents. Ingeneral, it is produced by jointly grinding the burnt cement clinkerwith other major and minor constituents.

The main raw material for clinker production is limestone which is minedin quarries, pre-comminuted in crushers and conveyed into the cementplant. After grinding and drying, it is mixed with other groundcomponents such as sand, clay or iron ore to obtain a raw meal. This rawmeal is burnt to clinker in a rotary kiln at temperatures above 1450° C.and then cooled in a cooler to a temperature of below 200° C.Subsequently, the granules obtained are ground to cement in a ball milltogether with gypsum or anhydrite (cf. “Integrated Pollution Preventionand Control (IPPC)”, Reference Document on Best Available Techniques inthe Cement and Lime Manufacturing Industries, European Commission,Brussels, 2011; Gasafi, E., Jeske, U. and T. Reinhardt, 2006,“Gipsreduktion mit Kohlenstoff-Rahmenbedingungen für die Verwertungmineralischer Reststoffe mit Sulfat and potentielle Einsatzstoffe fürein GRC-Verfahren”, publication series “Wissenschaftliche BerichteForschungszentrum Karlsruhe in der Helmholtz-Gemeinschaft” FZKA-7189,Karlsruhe).

According to a study of the World Business Council for SustainableDevelopment, the cement industry is responsible for about 5% of theglobal anthropogenic CO₂ emissions (cf. “The Cement CO₂ Protocol: CO₂Emissions Monitoring and Reporting, Protocol for the Cement Industry,Working Group Cement of the World Business Council for SustainableDevelopment (WGC-WBCSD), Oct. 19, 2001,http://www.wbcadcement.org/pdf/co2-protocol.pdf). Since about half ofthe CO₂ emissions during the clinker production are caused by the rawmaterial limestone, the reduction of the clinker content (clinkerfactor) by replacement of another component can provide a substantialcontribution to the reduction of these emissions.

As cement substitute, calcined clay was proposed for example. Thecalcination of fine-grained mineral solids, such as clay, conventionallyis effected in rotary kilns or multiple-hearth roasters. The maintenanceof a low temperature at a retention time necessary for the treatmentwith this method is ensured thereby. The U.S. Pat. No. 4,948,362 forexample describes a method for calcining clay, in which kaolin clay istreated in a multiple-hearth roaster by means of a hot calcining gas toincrease gloss and minimize abrasiveness. In an electrostaticprecipitator, the calcined clay powder is separated from the waste gasof the calcining furnace and processed further, in order to obtain thedesired product.

From DE 10 2008 031 165 A1 it is known to use the plant for producingthe cement itself for the production of calcined clay, wherein at leasttwo preheating lines are provided, of which one serves for preheatingthe clay and the other serves for heating clinker raw material. In acombustion chamber hot gases are produced, which serve the calcinationof the clay and are guided through the preheating stages in counterflowto the solids.

The clay used in these processes, however, has a high kaolin content ofmore than 40 wt-% and is very expensive, so that no economicallymarketable clinker substitute can be produced therefrom.

It is an object of the invention to provide a less expensive clinkersubstitute and based thereon less expensive cement, mortar and concrete,which in addition are characterized by a better CO₂ balance thanconventional construction materials.

It is another object of the invention to propose a less expensive way ofproducing a clinker substitute which in addition is characterized bylower CO₂ emissions.

This object substantially is solved with the invention by the featuresof claim 1, according to which the production of a clinker substitutefor use in the cement production is effected in the following steps:

a) predrying clay with an iron content >1.5 wt-% (indicated as Fe₂O₃)and a kaolinite content <40 wt-% to a moisture <10 wt-%, preferably <8wt-% and in particular <6 wt-%,

b) comminuting the clay to a grain size <2 mm, preferably <1 mm,

c) calcining the clay by thermal treatment in a furnace at a temperatureof 600 to 1000° C., preferably 700 to 900 ° C.,

d) thermal treatment of the clay under reducing conditions, inparticular by adding a CO-containing gas as reducing agent, at atemperature of 600 to 1000° C., preferably 700 to 900° C., wherein thereduction product is obtained,

e) intermediate cooling of the reduction product to a temperature <300°C.,

f) final cooling of the product, preferably directly with air and/orindirectly via cooling water.

In the sense of this description, the term “clay” preferably stands for“natural tempered pozzolan”, as defined in the standard DIN EN 197-1(German version: 2000, items 5.2.3 and 5.2.3.3) or the standard ASTMC618-05 (Class N).

After predrying and comminuting the clay, it is initially calcined atpreferably 600 to 900° C., wherein a phase change occurs and apozzolanically reacting clay of red color is produced. Pozzolans aresilicatic and alumosilicatic materials which hydraulically react withcalcium hydroxide (lime hydrate) and water and form calcium silicatehydrates and calcium alumina hydrates. These crystals are also obtainedduring the hardening (hydration) of cement and for example bring aboutthe strength and structural density of concrete. When calcining theclay, the maximum temperatures should be maintained, which uponexceedance thereof involve the risk of material sintering. In addition,at excessive temperatures the pozzolanic reactivity can get lost. Inaccordance with the invention, a temperature of 900° C. should thereforenot be exceeded permanently.

The method according to the invention itself is independent of the CaOcontent of the clay. For reducing sulfur emissions in a preferredembodiment, the clay used in step a) of the method according to theinvention has a CaO content of >0.1 wt-%, preferably >1.0 wt-%. Calciumis present in the raw material (educt) in the form of CaCO₃. In thecalcining process, it is converted to CaO by CO₂ —split-off and can bindSO₂, which possibly results from the combustion of sulfur-containingfuel, as CaSO₄.

By the subsequent reducing treatment with a CO-containing gas, a colorchange of the red calcined clay to grey calcined clay is effected due tothe reaction of the hematite (Fe₂O₃) contained in the clay to obtainmagnetite (Fe₃O₄) according to the equation

3 Fe₂O₃+CO=2Fe₃O₄+CO₂.

To ensure that this process proceeds sufficiently fast, it should takeplace at elevated temperatures >600° C., preferably >700° C.

As an inexpensive educt for producing the clinker substitute, a claywith an iron content >1.5 wt-% and preferably <4 wt-% (indicated asFe₂O₃) and a kaolinite content <40 wt-% is used in accordance with theinvention.

In accordance with a preferred aspect of the invention, the intermediatecooling of the reduction product in step e) is effected under oxygenexclusion, since the color is preserved thereby. The grey color of theclay finds high acceptance on the market, as the concrete color is notimpaired thereby. In accordance with the invention, cooling can beeffected by means of cooling screws, trickle coolers or the like.

In accordance with a development of the invention it is provided that inthe region under air exclusion oil can be injected, whereby in additiona reducing atmosphere is achieved, since the oil is gasified due to thehigh temperatures. Thus, the oil preferably serves to maintain reducingconditions.

The final cooling subsequently can be effected for example in afluidized-bed cooler, rotary tube cooler or the like with a suitablecoolant, e.g. with air.

In accordance with the invention, the calcination in step c) is effectedin a fluidized-bed reactor, a rotary kiln, a suspension calciner (flashcalciner) with a short retention time between 0.5 and 20 seconds,preferably between 1 second and 10 seconds, and in particular between 2and 8 seconds, or in a multiple-hearth roaster.

The necessary process heat is provided by the combustion of a fuel, suchas natural gas, petroleum or waste fuels. In accordance with theinvention, this is effected in an external combustion chamber, whereinthe combustion product produced is used for carrying out the thermaltreatment in step c) and/or d).

In accordance with a preferred embodiment, the combustion is effected inseveral stages, wherein the combustion in a first stage is operatedunder reducing conditions (lambda<1), in order to provide theCO-containing reduction gas for the color change from red to grey instep d). In a second stage, a complete combustion under air excess(lambda>1) then is effected. The hot gas generated here is supplied tothe calcining furnace in step c) with a temperature of about 950 to1200° C.

To make the calcination in step c) more economic, the clay is preheatedin one or more preheating stages in accordance with the invention priorto the calcination.

The invention also relates to a clinker substitute obtainable by themethod according to the invention as defined in claim 1.

A further subject-matter of this invention relates to a clinkersubstitute containing calcined clay, wherein the calcined clay contains<40 wt-% kaolinite and >1.5 wt-% iron in the form of iron oxides,preferably in the form of magnetite (Fe₃O₄). The clinker substituteaccording to the invention in particular is suitable for the productionof cement clinker, cement, mortar or concrete.

In a preferred embodiment, the clinker substitute according to theinvention consists of calcined clay, wherein the calcined clay contains<40 wt-% kaolinite and >1.5 wt-% iron in the form of iron oxides,preferably in the form of magnetite (Fe₃O₄). In the sense of thisinvention, the expression “consists of” is to be understood such thatthe clinker substitute exclusively contains calcined clay, i.e. 100%calcined clay.

In a further preferred embodiment, the clinker substitute containscalcined clay, wherein

-   -   the calcined clay is derived from hematite-containing clay, and    -   the hematite-containing clay contains >1.5 wt-% iron in the form        of hematite (Fe₂O₃) and <40 wt-% kaolinite,    -   wherein preferably the calcined clay contains >1.5 wt-% iron in        the form of iron oxides, but no iron in the form of hematite        (Fe₂O₃).

Preferably >90 wt-% of the iron oxides contained in the calcined clayare present as magnetite (Fe₃O₄). In a further preferred embodiment, >95wt-% and in particular >99 wt-% of the iron oxides contained in thecalcined clay are present as magnetite (Fe₃O₄). In a particularlypreferred embodiment of the clinker substitute according to theinvention, the calcined clay contains no hematite (Fe₂O₃). This meansthat in the calcined clay the hematite (Fe₂O₃) present in thehematite-containing clay preferably is quantitatively converted tomagnetite (Fe₃O₄).

Preferably, the calcined clay of the clinker substitute according to theinvention contains >0.1 wt-% CaO, preferably >1 wt-% CaO.

Subject-matter of the invention also is the use of the clinkersubstitute as partial replacement of Portland cement clinker for theproduction of Portland cement (CEM I) or Portland additive cement.Mortar and concrete can be produced therefrom.

A further subject-matter of this invention relates to a cement clinker,preferably Portland cement clinker, which contains the clinkersubstitute according to the invention.

Preferably, the cement clinker according to the invention contains 60 to90 wt-% conventional cement clinker and 10 to 40 wt-% clinkersubstitute, wherein the sum of the weight percentages of theconventional cement clinker and of the clinker substitute is 100 wt-%(the indicated weight percentages here are based on the total mass ofthe cement clinker).

The cement clinker according to the invention preferably is suitable forthe production of construction materials, such as cement, mortar andconcrete.

A further subject-matter of this invention relates to a cement,preferably Portland cement or Portland additive cement, which containsthe clinker substitute according to the invention.

Preferably, the cement according to the invention contains a cementclinker which contains 60 to 90 wt-% conventional cement clinker(preferably Portland cement clinker) and 10 to 40 wt-% clinkersubstitute according to the invention, wherein the sum of the weightpercentages of the conventional cement clinker and of the clinkersubstitute according to the invention is 100 wt-% (the indicated weightpercentages here are based on the total mass of the cement clinker).

The invention also extends to a mortar or concrete containing the cementaccording to the invention.

Finally, the invention comprises a method for producing a cement clinkeror a construction material containing cement clinker, wherein theconstruction material preferably is cement, mortar or concrete,comprising the step of: replacing 10 to 40 wt-%, preferably 15 to 35wt-%, more preferably 20 to 30 wt-%, and in particular 25 wt-% of aconventional cement clinker by the clinker substitute according to theinvention.

In a preferred embodiment, the invention comprises a method forproducing a construction material containing cement clinker, wherein theconstruction material preferably is cement, mortar or concrete,comprising the step of: replacing 10 to 40 wt-%, preferably 15 to 35wt-%, more preferably 20 to 30 wt-% and in particular 25 wt-% of acement by the clinker substitute according to the invention.

A structure containing the cement according to the invention, the mortaraccording to the invention and/or the concrete according to theinvention also is part of the present invention.

Further developments, advantages and possible applications can also betaken from the following description of exemplary embodiments and thedrawing. All features described and/or illustrated form thesubject-matter of the invention per se or in any combination,independent of their inclusion in the claims or their back-reference.

In the drawing:

FIG. 1 schematically shows the construction of a plant suitable forcarrying out the method according to the invention;

FIG. 2 shows a diagram of the compressive strength of the mortaraccording to the invention in dependence on the curing time and thecalcining temperature.

As starting material of the method according to the invention, clay withan iron content >1.5 wt-% (indicated as Fe₂O₃) and a kaolinite content<40 wt-% is used.

The following Table contains an overview of the preferred embodiments(Embodiment A to Embodiment T) concerning the content of iron, CaO andkaolinite, which preferably is contained in the educt:

Wt-% iron (indicated Wt-% Wt-% as Fe₂O₃) CaO kaolinite A >1.5 >0.1 <40B >1.5 >0.1 <35 C >1.5 >0.1 <30 D >1.5 >0.1 <25 E >1.5 >0.1 <20F >1.5 >0.1 <15 G >1.5 >0.1 <10 H >1.5 >0.1 <5 I >1.5 >0.1 <1J >1.5 >0.1 0 K >1.5 >1 <40 L >1.5 >1 <35 M >1.5 >1 <30 N >1.5 >1 <25O >1.5 >1 <20 P >1.5 >1 <15 Q >1.5 >1 <10 R >1.5 >1 <5 S >1.5 >1 <1T >1.5 >1 0

Further preferred embodiments concerning the content of iron, CaO andkaolinite, which is contained in the educt, are listed in the followingTable (Embodiment U to Embodiment Z):

Wt-% iron (indicated Wt-% Wt-% as Fe₂O₃) CaO kaolinite U >1.5 to 4 >0.1<40 V >1.5 to 4 >0.1 <20 W >1.5 to 4 >0.1 <10 X      2 to 3.5 >0.1 <40 Y     2 to 3.5 >0.1 <20 Z      2 to 3.5 >0.1 <10

In a non-illustrated pretreatment stage 1, the educt is coarselycomminuted to a grain size of <10 cm in a crusher and dried in a drierto a moisture of <6 wt-%. Subsequently, fine grinding is effected, e.g.in a hammer mill possibly with additional drying, to a grain size <1 mm.In doing so, a narrow grain range should be ensured. When graphicallydetermining the grain size distribution by means of an RRSB diagram(Rosin, Rammler, Bennet and Sperling) according to DIN 66145 the slope nshould lie in the range from 1 to 10.

After preheating in one or two preheating stages 2, 3, the clay thusprepared with a temperature of 350 to 600° C. is supplied to a calciningfurnace 4, e.g. in the form of a circulating fluidized bed, a rotarykiln, a flash calciner or a multiple-hearth roaster, and calcined thereat 600 to 900° C. To the calcining furnace 4, the clay recovered bydedusting 5 the waste gas of the preheating stage 2 and/or 3 can also besupplied.

Subsequent to the calcination, a change in color of the red calcinedclay into grey calcined clay is effected under reducing conditions in areduction furnace 6 (fluidized-bed furnace or rotary kiln), wherein thehematite (Fe₂O₃) contained in the clay, which causes the red color, isconverted to magnetite (Fe₃O₄). The change in color is effected attemperatures >600° C., preferably >700° C.

The reduction product thus obtained is cooled in a first cooling stage7, for example by means of cooling screws, trickle coolers or the like,under oxygen exclusion down to a temperature <300° C. In addition, oilcan be injected, in order to achieve a reducing atmosphere here as welldue to the oil gasifying at these temperatures.

Subsequently, a final cooling 8 can be effected in a fluidized bedcooler, rotary tube cooler or the like, for example with air.

Calcined clay is obtained, which can replace 10 to 40 wt-% of theclinker in cement. The CO₂ emissions thereby can be reduced by up to36%.

The necessary process heat is provided by the multi-stage combustion ofa fuel in an external combustion chamber 9. In a first stage 9a of thiscombustion chamber, the combustion process is operated under reducingconditions (lambda<1), in order to provide the reduction gas for thechange in color of the calcined clay from red to grey. In the secondstage, a complete combustion under air excess (lambda>1) then iseffected. The hot gas generated here is supplied to the calciningfurnace 4 with a temperature of 950 to 1200° C. Fresh air and/or in thesecond cooling stage 8 pre-heated air can be supplied to the combustionchamber 9 as combustion air.

A clinker substitute according to the invention contains calcined claywith <40 wt-% kaolinite and >1.5 wt-% iron in the form of iron oxides,preferably in the form of magnetite (Fe₃O₄). The clinker substituteaccording to the invention in particular is suitable for the productionof cement clinker, cement, mortar or concrete.

The calcined clay is derived from hematite-containing clay, wherein thehematite-containing clay contains >1.5 wt-% iron in the form of hematite(Fe₂O₃) and <40 wt-% kaolinite. Preferably, however, the calcined claycontains no more iron in the form of hematite (Fe₂O₃).

The hematite-containing clay (red clay) has a reddish color due to thehematite (Fe₂O₃) contained therein. This reddish color is not present inthe calcined clay (grey clay), since red hematite (Fe₂O₃) is convertedto black magnetite (Fe₃O₄). Preferably, the clinker substitute accordingto the invention is grey.

In a preferred embodiment, the weight ratio of black magnetite (Fe₃O₄)to red hematite (Fe₂O₃) in the clinker substitute according to theinvention or in the calcined clay is such that the clinker substituteaccording to the invention or the calcined clay does not have a reddishcolor, but is grey. Corresponding weight ratios can be determined by theskilled person by employing simple routine experiments.

Preferred embodiments (No.1 to No. 20) as regards the iron content andthe kaolinite content, which are contained in the clinker substitute orcalcined clay according to the invention, can be taken from thefollowing Table:

Wt-% Wt-% No. iron kaolinite 1 >1.5 <40 2 >1.5 <35 3 >1.5 <30 4 >1.5 <255 >1.5 <20 6 >1.5 <15 7 >1.5 <10 8 >1.5 <5 9 >1.5 <1 10 >1.5 0 11 >1.5to 4 <40 12 >1.5 to 4 <35 13 >1.5 to 4 <30 14 >1.5 to 4 <25 15 >1.5 to 4<20 16 >1.5 to 4 <15 17 >1.5 to 4 <10 18 >1.5 to 4 <5 19 >1.5 to 4 <120 >1.5 to 4 0

The content of iron indicated in the above Table refers to the contentof iron in the form of iron oxides, preferably to the content of iron inthe form of magnetite (Fe₃O₄).

Further preferred embodiments (No. 21 to No. 40) as regards the ironcontent and the kaolinite content, which are contained in the clinkersubstitute or calcined clay according to the invention, can be takenfrom the following Table:

Wt-% Wt-% No. iron kaolinite 21 2 to 3.5 <40 22 2 to 3.5 <35 23 2 to 3.5<30 24 2 to 3.5 <25 25 2 to 3.5 <20 26 2 to 3.5 <15 27 2 to 3.5 <10 28 2to 3.5 <5 29 2 to 3.5 <1 30 2 to 3.5 0 31 2.5 to 3 <40 32 2.5 to 3 <3533 2.5 to 3 <30 34 2.5 to 3 <25 35 2.5 to 3 <20 36 2.5 to 3 <15 37 2.5to 3 <10 38 2.5 to 3 <5 39 2.5 to 3 <1 40 2.5 to 3 0

The content of iron indicated in the above Table refers to the contentof iron in the form of iron oxides, preferably to the content of iron inthe form of magnetite (Fe₃O₄).

Preferably, >90 wt-% of the iron oxides contained in the calcined clayare present as magnetite (Fe₃O₄). In a further preferred embodiment, >95wt-% and in particular >99 wt-% of the iron oxides contained in thecalcined clay are present as magnetite (Fe₃O₄).

In a particularly preferred embodiment of the clinker substituteaccording to the invention, the calcined clay contains no hematite(Fe₂O₃). This means that in the calcined clay the hematite (Fe₂O₃)present in the hematite-containing clay preferably is quantitativelyconverted to magnetite (Fe₃O₄).

In a preferred embodiment, the calcined clay preferably contains >0.1wt-% CaO and <50 wt-% CaO, more preferably >0.1 wt-% CaO and <30 wt-%CaO, even more preferably >0.1 wt-% CaO and <20 wt-% CaO, mostpreferably >0.1 wt-% CaO and <10 wt-% CaO, and in particular >0.1 wt-%CaO and <5 wt-% CaO.

In a preferred embodiment, the calcined clay preferably contains >1 wt-%CaO and <50 wt-% CaO, more preferably >1 wt-% CaO and <30 wt-% CaO, evenmore preferably >1 wt-% CaO and <20 wt-% CaO, most preferably >1 wt-%CaO and <10 wt-% CaO, and in particular >1 wt-% CaO and <5 wt-% CaO.

Preferred embodiments (No. 41 to No. 60) as regards the iron content,kaolinite content and CaO content, which are contained in the clinkersubstitute or calcined clay according to the invention, can be takenfrom the following Table:

Wt-% Wt-% Wt-% iron kaolinite CaO 41 2 to 3.5 <40 0.1 to 5 42 2 to 3.5<35 0.1 to 5 43 2 to 3.5 <30 0.1 to 5 44 2 to 3.5 <25 0.1 to 5 45 2 to3.5 <20 0.1 to 5 46 2 to 3.5 <15 0.1 to 5 47 2 to 3.5 <10 0.1 to 5 48 2to 3.5 <5 0.1 to 5 49 2 to 3.5 <1 0.1 to 5 50 2 to 3.5 0 0.1 to 5 51 2.5to 3    <40 0.5 to 3 52 2.5 to 3    <35 0.5 to 3 53 2.5 to 3    <30 0.5to 3 54 2.5 to 3    <25 0.5 to 3 55 2.5 to 3    <20 0.5 to 3 56 2.5 to3    <15 0.5 to 3 57 2.5 to 3    <10 0.5 to 3 58 2.5 to 3    <5 0.5 to 359 2.5 to 3    <1 0.5 to 3 60 2.5 to 3    0 0.5 to 3

The content of iron indicated in the above Table refers to the contentof iron in the form of iron oxides, preferably to the content of iron inthe form of magnetite (Fe₃O₄).

In a particularly preferred embodiment, the calcined clay of the clinkersubstitute according to the invention contains 2 to 3.5 wt-% iron in theform of magnetite (Fe₃O₄), no hematite (Fe₂O₃), <25 wt-% kaolinite, and0.25 to 1.5 wt-% CaO.

In a preferred embodiment, no limestone is added to the clay, preferablyto the hematite-containing clay. The content of CaO in the clinkersubstitute according to the invention hence results from the calciumsalts such as CaCO₃ contained in the clay itself. In a further preferredembodiment, no kaolin is added to the clay, preferably to thehematite-containing clay. The content of kaolinite in the clinkersubstitute according to the invention hence results from the saltspresent in the clay itself.

In two particularly preferred embodiments (Embodiment 61 and Embodiment62), the hematite-containing clay comprises the following components:

Component Embodiment 61 Embodiment 62 SiO₂ 60 to 80 wt-% 65 to 75 wt-%TiO₂ 0.5 to 3 wt-% 1 to 2 wt-% Al₂O₃ 10 to 30 wt-% 15 to 25 wt-%Fe₂O₃ >1.5 to 5 wt-% 2 to 3.5 wt-% CaO 0.1 to 3 wt-% 0.4 to 2 wt-% MgO0.1 to 2 wt-% 0.1 to 1.2 wt-% K₂O 0.5 to 3 wt-% 0.5 to 2 wt-% Na₂O 0.1to 2 wt-% 0.1 to 1 wt-%

In two particularly preferred embodiments (Embodiment 63 and Embodiment64), the clinker substitute or calcined clay according to the inventioncomprises the following components:

Component Embodiment 63 Embodiment 64 SiO₂ 60 to 80 wt-% 65 to 75 wt-%TiO₂ 0.5 to 3 wt-% 1 to 2 wt-% Al₂O₃ 10 to 30 wt-% 15 to 25 wt-% Fe₂O₃ 0wt-% 0 wt-% Fe₃O₄ >1.5 to 5 wt-% 2 to 3.5 wt-% CaO 0.1 to 3 wt-% 0.4 to2 wt-% MgO 0.1 to 2 wt-% 0.1 to 1.2 wt-% K₂O 0.5 to 3 wt-% 0.5 to 2 wt-%Na₂O 0.1 to 2 wt-% 0.1 to 1 wt-%

The indication contained in the above Table that the content of Fe₂O₃ is0 wt-% means that the content of Fe₂O₃ lies below the detection limit ofthe X-ray fluorescence analysis (XRF). In a particularly preferredembodiment this indication means that no Fe₂O₃ is present in the clinkersubstitute according to the invention.

In a further particularly preferred embodiment, the clinker substituteor calcined clay according to the invention comprises the followingcomponents:

SiO₂  71 ± 3.0% TiO₂  1.7 ± 0.50% Al₂O₃  21 ± 2.0% Fe₂O₃ 0.0% Fe₃O₄ 2.8± 1.2% CaO 0.50 ± 0.25% MgO 0.60 ± 0.25% K₂O  1.3 ± 0.50% Na₂O 0.45 ±0.25%

The clinker substitute according to the invention preferably is used aspartial replacement of Portland cement clinker for the production ofPortland cement (CEM I) or Portland additive cement. Mortar and concretecan be produced therefrom.

Portland cement clinker and Portland cement (CEM I) are defined in thestandard DIN EN 197-1 (German version: 2000).

Preferably, the cement according to the invention, preferably Portlandcement or Portland additive cement, contains a clinker substitute whichcontains 60 to 90 wt-% conventional cement clinker (preferably Portlandcement clinker) and 10 to 40 wt-% clinker substitute according to theinvention, wherein the sum of the weight percentages of the conventionalcement clinker and of the clinker substitute according to the inventionis 100 wt-%.

Beside the clinker substitute according to the invention or the cementclinker according to the invention, the cement according to theinvention preferably also contains gypsum and/or anhydrite.

Preferably, 10 to 40 wt-%, more preferably 15 to 35 wt-%, even morepreferably 20 to 30 wt-%, most preferably 22 to 28 wt-%, and inparticular 24 to 26 wt-% of the total mass of cement are replaced(substituted) by the cement clinker according to the invention.

In a particularly preferred embodiment, 25 wt-% of the total mass ofcement are replaced by the cement clinker according to the invention.

Preferably, the cement clinker is Portland cement clinker. The cementpreferably is Portland cement or Portland additive cement.

In a preferred embodiment, the cement according to the inventioncontains no water (dry cement). In a further preferred embodiment, thecement according to the invention contains water, preferably in such aquantity that it can be employed for the respective use (ready-made).

The cement according to the invention preferably is suitable for theproduction of construction materials such as mortar and concrete.

A further subject-matter of the invention relates to mortar containing

-   -   the clinker substitute according to the invention as defined        above,    -   the cement clinker according to the invention as defined above,        or    -   the cement according to the invention as defined above.

Preferably, the mortar according to the invention is wall mortar,plaster, floor mortar or tile adhesive.

The mortar according to the invention preferably contains aggregatematerials, such as sand, fine gravel or wood chips or any mixturethereof. The mortar according to the invention in particular containssand.

Preferably, the maximum grain of the rock grain size of the usedaggregate materials sand and fine gravel is about 4 mm. The standard EN13139:2002 discloses the rock grain size for mortar.

In a preferred embodiment, the mortar according to the inventioncontains no water (dry mortar). In a further preferred embodiment, themortar according to the invention contains water, preferably in such aquantity that it can be employed for the respective use (ready-made).

A further subject-matter of the invention relates to concrete containing

-   -   the clinker substitute according to the invention as defined        above,    -   the cement clinker according to the invention as defined above,        or    -   the cement according to the invention as defined above.

Preferably the concrete according to the invention is lightweightconcrete, normal concrete, heavy concrete, reinforced concrete,prestressed concrete, fiber concrete or steel fiber concrete.

The concrete according to the invention preferably contains aggregatematerials, such as normal aggregate, lightweight aggregate or heavyaggregate or any mixture thereof. In a preferred embodiment, theconcrete according to the invention contains no water. In a furtherpreferred embodiment, the concrete according to the invention containswater, preferably in such a quantity that it can be employed for therespective use (ready-made).

In the sense of this description the term “normal aggregate” comprisesaggregates with a bulk density of 2200 to 3200 kg/m³. Preferably, theseare of course aggregate materials (e.g. sand with a preferred grain sizeup to 2 mm, gravel from river deposits and moraines, crushed stone,grit, crushed sand, filler, mineral powder) or artificial aggregatematerials (e.g. blast furnace slag, crushed clinker, concrete grit).

In the sense of this description the term “lightweight aggregate”comprises aggregate materials with a bulk density <2200 kg/m³.Preferably, these are natural lightweight aggregates (e.g. pumice, lavasand, lava gravel, diatomaceous earth) or artificial lightweightaggregates (e.g. expanded shale, expanded clay, foamed slag).Lightweight aggregates preferably are used for the production oflightweight concrete.

In the sense of this description the term “heavy aggregate” comprisesaggregates with a bulk density >3200 kg/m³. Preferably, these arenatural aggregate materials (e.g. heavy spar, magnetite, hematite,limonite) or artificial aggregate materials (e.g. crushed stone,heavy-metal slags). Heavy aggregates preferably are used for theproduction of heavy concrete.

The standard EN 12620:2003-04 discloses the rock grain size forconcrete.

A further subject-matter of this invention relates to a method forproducing cement or a construction material containing cement, whereinthe construction material preferably is mortar or concrete, comprisingthe step of: replacing 10 to 40 wt-%, preferably 15 to 35 wt-%, morepreferably 20 to 30 wt-% and in particular 25 wt-% of a conventionalcement clinker, preferably Portland cement clinker, by the clinkersubstitute according to the invention.

A preferred subject-matter of this invention relates to a method forproducing cement or a construction material containing cement, whereinthe construction material preferably is mortar or concrete, comprisingthe step of: replacing 10 to 40 wt-%, preferably 15 to 35 wt-%, morepreferably 20 to 30 wt-% and in particular 25 wt-% of a conventionalcement, preferably Portland cement or Portland additive cement, by theclinker substitute according to the invention.

The conventional cement clinker preferably is a cement clinker on thebasis of limestone (e.g. Portland cement clinker). Preferably, theconventional cement clinker hence contains limestone in a highconcentration and thus also a high CaO content of usually >55 wt-%, inparticular about 58 wt-% up to about 66 wt-%.

The conventional cement clinker can be a cement clinker which containskaolin.

Preferably, the conventional cement clinker is Portland cement clinker.

In a preferred embodiment, the method according to the invention forproducing the cement according to the invention comprises the followingsteps:

a) replacing 10 to 40 wt-%, preferably 15 to 35 wt-%, more preferably 20to 30 wt-% and in particular 25 wt-% of a conventional cement clinker,preferably Portland cement clinker, by the clinker substitute accordingto the invention,

b) admixing gypsum or anhydrite.

If necessary, the mixture obtained in step b) can be ground. By means ofthis method, dry cement according to the invention preferably isobtained in powder form. The dry cement obtained in step b) can also bemixed with water, in order to preferably obtain ready-made cement.

In a further preferred embodiment, the method according to the inventionfor producing the cement according to the invention comprises thefollowing step: replacing 10 to 40 wt-%, preferably 15 to 35 wt-%, morepreferably 20 to 30 wt-% and in particular 25 wt-% of a conventionalcement, preferably Portland cement or Portland additive cement, by theclinker substitute according to the invention. If necessary, the mixtureobtained in this step can be ground. By means of this method, dry cementaccording to the invention preferably is obtained in powder form. Thedry cement obtained can also be mixed with water, in order to preferablyobtain ready-made cement.

In a preferred embodiment, the method according to the invention forproducing the mortar according to the invention comprises the followingstep: mixing the cement according to the invention with aggregatematerial, preferably sand, fine gravel or wood chips or any mixturethereof. Preferably, the dry mortar produced by this method is convertedinto ready-made mortar by adding water.

In a preferred embodiment, the method according to the invention forproducing the mortar according to the invention comprises the followingsteps:

a) replacing 10 to 40 wt-%, preferably 15 to 35 wt-%, more preferably 20to 30 wt-% and in particular 25 wt-% of a conventional cement clinker,preferably Portland cement clinker, by the clinker substitute accordingto the invention,

b) admixing gypsum or anhydrite,

c) admixing aggregate material to the mixture obtained in step b),wherein the aggregate material preferably is sand, fine gravel or woodchips or any mixture thereof.

If necessary, the mixture obtained in step b) can be ground. By means ofthis method, the corresponding dry mortar according to the invention isproduced.

In a further preferred embodiment, the method according to the inventionfor producing the mortar according to the invention comprises thefollowing steps:

a) replacing 10 to 40 wt-%, preferably 15 to 35 wt-%, more preferably 20to 30 wt-% and in particular 25 wt-% of a conventional cement,preferably Portland cement or Portland additive cement, by the clinkersubstitute according to the invention,

b) admixing aggregate material to the cement obtained in step a),wherein the aggregate material preferably is sand, fine gravel or woodchips or any mixture thereof.

If necessary, the mixture obtained in step a) can be ground. By means ofthis method, dry mortar is produced.

Preferably, the maximum grain of the rock grain size of the usedaggregate materials sand and fine gravel is about 4 mm. The standard DINEN 13139:2002 discloses the rock grain size for mortar.

In a particularly preferred embodiment, the aggregate material is sand.

By mixing the cement according to the invention with the aggregatematerial (sand, fine gravel or wood chips or any mixture thereof)without the addition of water, dry mortar according to the invention isobtained. By adding water to the dry mortar according to the invention,the ready-made mortar according to the invention is obtained.

In a preferred embodiment, the method according to the invention forproducing the concrete comprises the following step: mixing the cementaccording to the invention with aggregate material, preferably normalaggregate, lightweight aggregate or heavy aggregate or any mixturethereof. Preferably, the dry concrete produced by this method isconverted into ready-made concrete by the addition of water andsubsequent mixing.

In a preferred embodiment, the method according to the invention forproducing the concrete according to the invention comprises thefollowing steps:

a) replacing 10 to 40 wt-%, preferably 15 to 35 wt-%, more preferably 20to 30 wt-% and in particular 25 wt-% of a conventional cement clinker,preferably Portland cement clinker, by the clinker substitute accordingto the invention,

b) admixing gypsum or anhydrite,

c) mixing the mixture obtained in step b) with aggregate material,preferably normal aggregate, lightweight aggregate or heavy aggregate orany mixture thereof.

If necessary, the mixture obtained in step b) can be ground. Preferably,water is added to the mixture obtained in step c), in order to obtainready-made concrete.

In a further preferred embodiment, the method according to the inventionfor producing the concrete according to the invention comprises thefollowing steps:

a) replacing 10 to 40 wt-%, preferably 15 to 35 wt-%, more preferably 20to 30 wt-% and in particular 25 wt-% of a conventional cement,preferably Portland cement or Portland additive cement, by the clinkersubstitute according to the invention,

b) mixing the cement obtained in step a) with aggregate material,preferably normal aggregate, lightweight aggregate or heavy aggregate orany mixture thereof.

If necessary, the mixture obtained in step a) can be ground. Preferably,water is added to the mixture obtained in step b), in order topreferably obtain ready-made concrete.

In this connection, the terms “normal aggregate”, “lightweightaggregate” and “heavy aggregate” are used as already defined above. Themethod steps “mixing” and “grinding” mentioned in the methods disclosedabove can be carried out with all suitable devices for mixing andgrinding. Suitable devices are known to the skilled person. For example,for grinding in the cement production a ball mill preferably is used. Inthe production of the above-mentioned construction materials concretemixers or drum mixers can be used.

The cement according to the invention, the mortar according to theinvention and the concrete according to the invention are suitable inparticular for building structures.

A further subject-matter of the invention relates to a structurecontaining the clinker substitute according to the invention as definedabove, the cement clinker according to the invention as defined above,the cement according to the invention as defined above, the mortaraccording to the invention as defined above and/or the concreteaccording to the invention as defined above.

In the sense of this description, the term “structure” preferablycomprises buildings (e.g. residential house, skyscraper, church, factoryhall, stable, greenhouse, warehouse, garage), traffic structures (e.g.bridge, street, tunnel, gallery), supply and waste disposal structures(e.g. water and sewage conduits, chimneys, sewage disposal plants, dike,retaining dam, masonry dam, weir, transmission towers, transmissionmasts, aerial line masts), protective buildings (e.g. protectiverampart, protective dam, avalanche control, gallery, shelter), defenseand fortification systems (e.g. fortification, defense tower) andtemporary structures.

EXAMPLES Material used

The clay was obtained from a clay pit in Southern Brandenburg (Germany).

Pretreatment

The material was dried over night at 70° C. in a drying cabinet. Thedried clay was ground in a jaw crusher to a particle size of less than 6mm and subsequently ground in a disk mill to a particle size of lessthan 1 mm. The comminuted clay particles were screened and material witha particle size of less than 1 mm was used for the further testingprocedures.

Chemical composition and physical parameters

The chemical composition of the samples was determined by X-rayfluorescence analysis (XRF). The results of this analysis are shown inthe following Table:

SiO₂ 71.71% TiO₂ 1.72% Al₂O₃ 20.90% Fe₂O₃ 2.81% CaO 0.51% MgO 0.63% K₂O1.29% Na₂O 0.43%

The loss on ignition (LOI) indicates the loss of mass of the sample dueto the release of volatile substances (the sample was heated to 1050°C., until a constant weight loss was detected). In the case of clay, thevolatile substances chiefly comprise water and for a small part carbondioxide. The specific gross weight of the samples was determined to be1.13 kg/I.

Particle Size Distribution

The particle size distribution was determined with a screen tower inconjunction with an air-swept screen for small particles smaller than100 μm. The clay had a mean particle diameter d20 of 100 μm, d50 of 192μm and a Sauter diameter dSauter of 130 μm.

Production

The reactor comprises a steel tube with an inside diameter of 80 mm anda height of 1.5 m. The reactor shell contains three independentlycontrolled electric heating systems. Cyclone 1 and cyclone 2 areinsulated and electrically heated. The clay starting material isintroduced with a metering screw. The product is dischargedsemi-continuously through a ball valve at the bottom of the reactor.Fluidizing gas is introduced and analysed with flow meters. The gas iselectrically heated to about 650° C. and then flows through the grating.Additional air (purge gas) is let in at six different points in smallquantities. The waste gas is guided to a waste gas filter.

The temperatures are measured at three different points at differentheights of the reactor and in the recycle cyclone by means of Ni—Cr—Niheating elements. The retention time and execution of the manual productwithdrawal are controlled by measuring the pressure difference betweenthe upper and the lower end (above the nozzles) of the reactor. Theabsolute pressure inside the reactor is approximately atmospheric.

The reactor and the cyclones are inspected and cleaned before each testseries. The apparatus was subsequently heated up. After the desiredtemperature has been reached, the clay starting material was introducedinto the reactor by means of a metering screw. After the desiredpressure difference in the reactor has been reached, the ball valve wasopened for a short time, in order to discharge the product(semi-continuous withdrawal).

The reactor subsequently was operated for approximately one hour at thedesired pressure difference, in order to obtain a homogeneous productconcentration with sufficient retention time. Samples were taken fromthe bed and the second cyclone.

Results

a) Test parameters

The calcination could be carried out by means of the desired testparameters.

The following Table provides an overview of the test parameters (averagevalues under steady-state conditions):

Test 1 Test 2 Test 3 Test 4 Temperature ° C. 650 700 750 850 Δp mbar 2121 21 20 Feed rate kg/h 1.4 3.0 3.0 2.8 V. air Nm³/h 2.2 2.2 2.2 2.2

b) Retention time and gas velocity

The retention time τ was calculated as follows:

${\tau = \frac{{dp} \cdot A}{g \cdot m_{R}}},$

wherein

τ: retention time [min]

dp: pressure difference over the reactor height [Pa]

A: diameter of the CFB [m²]; A=0.005 m²

g: gravitational acceleration

m_(R): mass flow rate of the charge or actual withdrawal [kg/min]

The calculated retention times based on the input of material are

-   -   45 min for Test 1    -   22 min for Tests 2, 3 and 4.

c) Loss on ignition after calcination

The loss on ignition (LOI) was determined for all calcined clay sampleswhich were taken from the bed. The test specimens were heated to 1050°C. and left under these conditions, until a constant weight loss wasdetected.

In all measurement series, the loss on ignition in the product is lessthan 1 wt-% and decreases with increasing temperature. The loss onignition for the material taken from the cyclone is greater due to thereduced retention time of the material. At 700° C. bed material andcyclone material have approximately identical values. It was found thatthere is a trend towards a decreasing loss on ignition with increasingtemperature.

d) Compressive strength of the mortar samples according to DIN EN 196-1

The calcined clay samples produced by the above method were tested formortar compressive strength after 7 and 28 days corresponding to DIN EN196-1 (German version: 1994).

The strength test was carried out according to DIN EN 196-1 (Germanversion: 1994). In the standard mixtures, the cement was eachsubstituted for 25% by the material samples. The mortar samples wereproduced according to DIN EN 196-1 (German version: 1994). The testingarea for the compressive strength test (carried out on half prisms) was40×40 mm after 7 days corresponding to DIN EN. After 28 days, thetesting machine had to be changed due to the high sample strength andthus the changed testing range, wherein the testing area now was 40×65mm. A smaller testing area in general leads to higher strength values.However, since the reference samples of 100% cement were tested in thesame way, nothing is changed in the statement as to the quality of thematerial. As cement—contrary to the standards and test specifications—aCEM I 52.5 R was used instead of a CEM I 42.5 R.

FIG. 2 shows the results of the compressive strength test of the mortarprisms after 7 and 28 days.

As a result it was found that all mortar samples satisfy the strengthsfor an additive cement CEM II 52.5 required according to DIN EN 196-1after 28 days, i.e. all individual values lie above 52.5 N/mm² and themean values lie above 61 N/mm². Of the mortars, sample 2 (700° C.) showsthe highest strength, after 28 days with 65 N/mm². The criteria toachieve 70% and 75%, respectively, of the cement strengths(specification corresponding to the DIBt approval principles foradditives or ASTM C618-05) were satisfied by all materials both after 7and after 28 days.

LIST OF REFERENCE NUMERALS

1 pretreatment

2 first preheating stage

3 second preheating stage

4 calcining furnace

5 dedusting

6 reduction furnace

7 first cooling stage

8 second cooling stage

9 combustion chamber

9 a first stage

9 b second stage

1-21. (canceled)
 22. A method for producing a clinker substitute for usein cement production, the method comprising; a) predrying clay with aniron content >1.5 wt-% in a form of iron oxides and a kaolinite content<40 wt-.% to a moisture <10 wt-%; b) comminuting the clay to a grainsize <2 mm; c) calcining the clay by thermal treatment in a furnace at atemperature of 600 to 1000° C.; d) thermally treating the clay underreducing conditions at a temperature of 600 to 1000° C. so as to form areduction product; e) intermediately cooling the reduction product to atemperature <300° C.; and f) finally cooling the reduction product. 23.The method according to claim 22, wherein a clay with an ironcontent >1.5 wt-% in the for of iron oxides, a CaO content >0.1 wt-%,and a kaolinite content <40 wt-% is used as an educt.
 24. The methodaccording to claim 22, wherein the intermediate cooling of the reductionproduct in step e) is effected under oxygen exclusion.
 25. The methodaccording to claim 22, wherein, during the intermediate cooling of thereduction product in step e), oil is introduced as an additionalreducing agent.
 26. The method according to claim 22, wherein thecalcination in step c) is effected in a fluidized-bed reactor, a rotarykiln, a suspension calciner or a multiple-hearth roaster.
 27. The methodaccording to claim 22, wherein in an external combustion chamber a fuelis burnt and a combustion product produced is used for carrying out thethermal treatment in at least one of steps c) and d).
 28. The methodaccording to claim 27, wherein the combustion is carried out in aplurality of stages including at least one first stage in which thecombustion is effected under reducing conditions and at least one secondstage in which the combustion is effected under oxidizing conditions.29. The method according to claim 28, wherein a combustion productproduced in the at least one first stage is used as reduction gas duringthe thermal treatment in step d).
 30. The method according to claim 28,wherein a combustion product produced in the at least one second stageis used as hot gas during the calcination in step c).
 31. The methodaccording to claim 22, wherein the clay is preheated in one or morepreheating stages prior to the calcination.
 32. A clinker substitutecontaining calcined clay, wherein the calcined clay contains <40 wt-%kaolinite and >1.5 wt-% iron in a form of iron oxides, and wherein >90wt-% of the iron oxides contained in the calcined clay are present asmagnetite (Fe₃O₄).
 33. The clinker substitute according to claim 32,wherein the calcined clay contains no hematite (Fe₂O₃).
 34. The clinkersubstitute according to claim 32, wherein the calcined claycontains >0.1 wt-% CaO.
 35. The clinker substitute according to claim32, wherein no limestone or no kaolin is added to the clay.
 36. Theclinker substitute according to claim 32, wherein the clinker substituteis present in cement, mortar or concrete.
 37. Cement containing theclinker substitute according to claim
 32. 38. Mortar or concretecontaining the cement according to claim
 37. 39. A method for producinga cement clinker or a construction material containing the cementclinker, wherein the construction material is cement, mortar orconcrete, comprising the step of replacing 10 to 40 wt-% of aconventional cement clinker by the clinker substitute according to claim32.
 40. A structure containing the mortar or cement according to claim37.